Multiband Power Amplifier Bias Control for Lower AM-PM Distortion
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Solution Overview
Problem
Existing power amplifier modules in multiband communications systems face high current consumption and AM-PM distortion issues due to fixed bias current settings, which are not adaptive to varying signal power levels across different frequency bands.
Innovation Solution
A power amplifier apparatus with an envelope tracking (ET) current bias circuit that generates a first ET bias current by calculating direct and ET currents based on a reference voltage and ET voltage, with adjustable ratios to maintain a constant average current, reducing AM-PM distortion and improving efficiency across different bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed bias current is provided to the power amplifier, then the amplifier can maintain stable operation across different bands, but the current consumption increases and AM-PM distortion occurs when signal power varies
Solution Approach 1:
The patent implements dynamic bias current adjustment by providing different bias current values corresponding to different frequency bands and signal power levels. The bias current is no longer fixed but adapts dynamically based on operating conditions, resolving the contradiction between stable operation and reduced current consumption.
Solution Approach 2:
The patent changes the bias current parameter according to frequency band and signal power level. By adjusting this critical parameter dynamically, the system achieves both stable operation across bands and reduced current consumption when signal power is low, while preventing AM-PM distortion through appropriate biasing.
2Reliability
If a fixed bias current is provided to the power amplifier, then the amplifier operates reliably across bands, but AM-PM distortion characteristics deteriorate when signal power varies
Solution Approach 1:
The patent dynamically adjusts the bias current based on signal power level and frequency band to maintain optimal amplifier operation. This dynamic adjustment prevents AM-PM distortion by ensuring the amplifier remains in its linear region even when signal power varies, while maintaining reliable operation across different bands.
Solution Approach 2:
The patent implements a feedback mechanism where the bias current is adjusted based on the detected signal power level and frequency band. This feedback control ensures that the bias current is always appropriate for the current operating conditions, preventing AM-PM distortion while maintaining stable operation.
3Loss of energy
If envelope tracking is used to reduce current consumption, then efficiency improves at low signal power, but the system lacks adaptive bias current control for further optimization
Solution Approach 1:
The patent extends the envelope tracking concept to bias current control, making the bias current dynamic and adaptive rather than fixed. This allows further optimization of current consumption beyond what envelope tracking alone achieves, while improving the system's adaptability to different operating conditions through multi-band, multi-power-level bias adjustment.
Data Source
AI summary
A power amplifier apparatus, includes an envelope tracking (ET) current bias circuit configured to generate a first ET bias current by calculating a direct current DC, based on a reference voltage, and an ET current, based on an ET voltage, according to an envelope of an input signal; and a power amplifier circuit having a bipolar junction transistor supplied with the first ET bias current and a power voltage to amplify the input signal, wherein an average current of the first ET bias current is controlled to be substantially constant.